1. Field of the invention
The present invention relates to a metal elastic member, a miniature machine, a method of manufacturing a miniature machine, a swing control device, and a swing control method, and, for example, relates to a metal elastic member, a miniature machine, a method of manufacturing a miniature machine, a swing control device, and a swing control method which are used for repetitively scanning light within a predetermined angle range.
2. Description of the related art
A miniature machine such as a scanning light deflection element to be manufactured by using the MEMS (Micro Electro Mechanical Systems) technique includes at least one movable unit, a fixed unit, and paired beams for supporting the movable unit at the respective ends with respect to the fixed unit. The movable unit is supported by the fixed unit so as to be swingable about an axis with paired beams serving as torsional rotation axes. In other words, the beams serve as torsion beams in a gimbal structure.
For example, in a miniature machine in which the movable unit is configured by a light deflecting mirror for deflecting and scanning incident light and a flat coil formed on a back face of the light deflecting mirror and paired permanent magnets are disposed in the fixed unit so as to have the coil sandwiched therebetween, Lorentz force generated by an alternating current flowing to the coil and a magnetic field formed by the permanent magnets acts on the coil so that the movable unit supported by the beams, that is, the light deflecting mirror is repetitively swung.
Japanese Unexamined Patent Publication No. 2003-84226 proposes an optical scanner having a movable unit and a beam formed integrally by applying a semiconductor manufacturing technique to a single crystal silicon substrate.
Japanese Unexamined Patent Publication No. 9-281417 proposes a micro mirror device in which a beam is fabricated by using a conductive amorphous aluminum alloy in a monolithic manufacturing process.
Japanese Unexamined Patent Publication No. 2009-175368 proposes a vibration mirror including a beam obtained by pressing pure titanium or a titanium alloy.
Japanese Unexamined Patent Publication No. 2008-40228 discloses a miniature machine including a beam formed by a conductive polymer as a suitable beam for driving a movable unit at a low frequency of 150 Hz or less. The miniature machine is used for a bar code reader or the like and serves to scan measurement light at a light deflection angle of approximately 50°.
Moreover, Japanese Unexamined Patent Publication Nos. 2004-258548 and 2012-170196 disclose a control method of variably controlling the value of current applied to a coil in order to control to swing the movable unit of the miniature machine at certain amplitude.
In a case where there is configured a small-sized scanning type distance measuring device using the light deflecting mirror or an obstacle detecting device using the scanning type distance measuring device, it is necessary to swing a deflecting mirror of several mm square at a comparatively low frequency of 150 Hz to 500 Hz, thereby scanning with measurement light within a scanning angle range of 45°, for example.
However, the beam fabricated by using a silicon material described in Japanese Unexamined Patent Publication No. 2003-84226 is a suitable material for a case where it is necessary to drive the movable unit at a comparatively high frequency, and has a problem in that stable driving cannot be carried out at a frequency of 500 Hz or less. Since the silicon material causes cleavage comparatively easily, moreover, there is also a problem in that the silicon material is hard to be used for a demand of a shock resistance.
The beam using the conductive amorphous aluminum alloy described in Japanese Unexamined Patent Publication No. 9-281417 has a problem in that the beam is fabricated in the monolithic manufacturing process so that a manufacturing cost is increased, and furthermore, has a problem in that the beam is hard to use in measurement requiring a beam diameter to some extent because a size including a light deflecting mirror of about 10 to 20 μm square is very small.
Referring to the beam obtained by pressing a metal described in Japanese Unexamined Patent Publication No. 2009-175368, a large number of minute concavo-convex portions or scratches are formed on a surface thereof in the working and stress concentrates depending on stress amplitude thereon. For this reason, there is a problem in that the minute concavo-convex portions or scratches act as starting points to grow a crack due to repetitive use and a fatigue failure thus tends to occur.
In particular, an optical scanner for scanning with measurement light to detect the presence of an obstacle based on reflected light corresponding to the measurement light is operated continuously for a long period of time. For this reason, even if the optical scanner is used at a frequency of 100 Hz, for example, it is necessary to resist stress amplitude three billion times per year.
For this reason, these metal components are usually subjected to a life test tens of thousands of times to hundreds of thousands of times or millions of times to tens of millions of times, and the life test for several tens of hours or several hundreds of hours in conversion into a time, and are used within a range in which a safety factor calculated based on the result is taken into consideration. In recent years, however, it is indicated that the safety factor is lacking in evaluation depending on stress amplitude millions of times to tens of millions of times.
A crack originating from a scratch on a surface or the like is referred to as a high cycle fatigue and a crack originating from a crystal defect in an inner part or the like is referred to as a Very High Cycle Fatigue, and a test hundreds of millions of times or billions of times of tests are required for evaluation. Consequently, a time required for the test also becomes enormous and it is actually difficult to guarantee a life to that extent.
The beam formed by a conductive polymer described in Japanese Unexamined Patent Publication No. 2008-40228 exhibits a preferred characteristic at a low frequency of 150 Hz or less. However, there is a problem in that stable driving cannot be carried out at a frequency of 150 Hz to 500 Hz, and a stress rupture is apt to be caused if hardness of a polymer is increased to aim at the stable driving.
As described in Japanese Unexamined Patent Publication Nos. 2004-258548 and 2012-170196, in the case where the value of current applied to the coil is variably controlled in order to control to swing the movable unit of the miniature machine at certain amplitude, there is required a complicated large-scale power supply circuit for accurately controlling the applied current value including a factor for a change in a temperature characteristic of a circuit element or the like. Consequently, there is also a problem in that a cost is increased, and furthermore, a large installation space is required.